In the employment of cylinders for the storage of high pressure fluids, particularly gasses, it is common practice to furnish the neck of the cylinder with a female thread into which some form of dispensing valve is fitted. This valve then holds the high-pressure gas charge within the cylinder and enables it to be dispensed when required by manipulating a handle or similar. By the nature of their function, such dispensing valves must be robust, in order to safely contain the high pressure within the cylinder. Robustness is also of particular importance to ensure that the cylinder, with its fitted valve, can withstand the physical abuse which inevitably occurs during handling, particularly during transport and refilling operations. Should the valve be subject to excessive mishandling so that it is sheared off or broken away from the cylinder, then a sudden release of high-pressure stored gas can result, with all of the attendant dangers—for example the cylinder can become a high velocity projectile propelled by the escaping gas.
These dangers have become more acute with the recent use of modern wrapping materials, such as carbon fibre filaments, to manufacture high pressure gas cylinders from light materials such as aluminium. As a result of these developments, the situation has arisen whereby the ‘top hamper’ (which is understood to include the gas control devices fitted to the cylinder including dispensing valves, any regulator fitted, together with any conserving devices), can be heavier than the cylinder itself, even when the cylinder is filled with gas.
In addition, the size of the top hamper can be considerable, sometimes even comparable to that of the cylinder itself, in the case of the smaller-sized cylinders, and this renders the cylinders vulnerable to damage during handling, storage and transport. For example, many designs of dispensing valve are so tall that they protrude to a sometimes considerable extent above the neck of the cylinder itself, and are thus particularly vulnerable to damage. One way of overcoming this problem is to provide that, should the top part of the valve be broken away, a self closing stop valve will operate to retain the pressurised gas within the cylinder. One example of such an arrangement is described in U.S. Pat. No. 4,077,422 which discloses a fail-safe shut-off device. In this device a valve spool is maintained in a balanced state by means of the pressure in a liquid situated in a chamber extending above the neck of the cylinder against the pressure provided by the combined effect of the compressed gas stored within the cylinder and a coil spring. A narrowed area provides a zone of weakness at which shearing off of the dispensing valve preferentially occurs in the event of an incident and, upon fracture at this point, pressure in the liquid is lost, and the valve spool moves onto a valve seat to thereby close off the cylinder. A particular disadvantage of this arrangement is that the weakened zone can in itself be a hazard because it makes the top hamper more likely to break off in the event of mistreatment such as if the cylinder is dropped or the top part hit.
Another example is described in U.S. Pat. No. 6,230,737 which uses a check valve which is permanently screwed into the threaded mouth of the cylinder and on which a dispensing valve may be mounted. The dispensing valve incorporates a stem which acts on the check valve to keep it open while the dispensing valve is in place. The lower profile of the cylinder when not fitted with the dispensing valve does reduce the opportunity for damage or breakage, but even the check valve itself extends significantly above the cylinder neck and therefore remains vulnerable.
Similar arrangements of dispensing valve and stop valve are to be found in other patents such as U.S. Pat. No. 5,144,973, U.S. Pat. No. 5,894,859, U.S. Pat. No. 3,930,517 and U.S. Pat. No. 4,907,617.
In the present invention the stop valve is replaced by a balanced valve such as described in GB-A-2298026 and WO 2004/051388. Such valves, whilst capable of acting as a stop valve for the potentially high pressures within the cylinder, require a relatively low actuating force so that they can be used directly with an associated reaction piston or diaphragm within a regulator mounted on the cylinder. Such an arrangement is more versatile than prior art arrangements, enabling a variety of different fittings, such as dispensing valves, regulators or filling devices, to be assembled to the cylinder secure in the knowledge that, should the fitting be dislodged or damaged, the balanced valve will close to secure the cylinder.
In addition, when used as a regulator valve, in conjunction with a regulator actuator, the balanced valve is found to be more tolerant of the large differences in pressure ratio across the valve which occur as between a cylinder which is fully pressurised with fluid and one which is nearly empty. With a non-balanced valve, the regulated pressure tends to drop off to an unusable level long before the cylinder is actually empty so the full fill of gas is, in effect, not available. Even before this, there is also a small, but noticeable fall off in regulated pressure as the cylinder empties.
Furthermore, when used in conjunction with a regulator, a balanced valve gives the advantage that it will intrinsically allow the fluid in the cylinder to be substantially completely discharged. Commercially available regulators which do not use a balanced valve are unable to completely empty the cylinder and flow will cease when the pressure in the cylinder falls to about 100 psi. There are times when it can be desirable to completely discharge the cylinder. In diving cylinders, for example, there may be situations where the full volume of the fluid in the cylinder may need to be made available.
FIG. 1 of the accompanying drawings shows one version of the balanced valve described in GB-A-2298026 and WO 2004/051388. The valve comprises a hollow cylindrical body 1 having an external threaded section 2 and an O-ring 3 for sealing purposes Mounted within the hollow interior of the body 1 is a piston 4 which is attached to a support member 5 fitted in a recess at the lower end of the body 1 and secured in place by a circlip 6. Slidably mounted over the piston 4 is a valve member or poppet 7. An annular seal 12 seals the underside of piston 4 against valve member 7. A spring 8 acting between the piston 4 and the closed-off upper end of the valve member 7 acts to urge the valve member 7 in an upwards direction relative to the valve body 1. The valve member 7 is formed with a narrow upper portion and a wider lower portion, between which is a conical section carrying a layer 9 of resilient sealing material. The action of the spring 8 is such as to urge this sealing layer 9 against the edge of an annular shoulder 10 formed in the interior of the body 1.
The upper part of the body 1 is formed as a shroud 11 which defines an upper chamber 13 from which gas emerges transversely, as indicated. In use, high pressure gas enters the valve from beneath, via inlet passageways 14 through the support member 5, thence passes through the interior of the valve body 1 round the exterior of the valve member 7, via the valve seat 9/10, if open, and into the chamber 13 on the low pressure side of the valve. Apertures 15 in the upper part of the valve member 7 provide communication between the chamber 13 and the interior of the valve member 7 above the piston 4, so that the upper side of piston 4 is exposed to the low pressure side of the valve.
In the arrangement shown, the diameter 16 of the lower (wider) part of the valve member 7 is substantially equal to the inner diameter 17 of the valve seat 9/10 so that, when the valve is in the closed position (as shown), the gas pressure on the low pressure side of the valve produces no net force on the valve member 7 and likewise, neglecting the finite width of the valve seat, the gas pressure on the high pressure side of the valve produces no net force on the valve member 7. The valve is thus balanced. Further detail concerning the construction and operation of the valve can be obtained from the aforementioned patents.
As well as the balanced action, a further advantage of a valve of this type is that it provides a valve seat which allows a substantially greater gas flow rate than is practicable with non-balanced valves. In addition the valve does not extend into the storage volume of the cylinder at all and thus does not use up valuable storage capacity. This contrasts with many prior art valve arrangements, such as typified by that described in U.S. Pat. No. 5,894,859 in which a useful proportion of the storage capacity is occupied by the valve, and its associated equipment. This problem is particularly acute with smaller sized cylinders that can range in capacity from 150 liters down to as little as 0.6 liters or less.
Furthermore, the relatively small size and the manner of fitting of this type of valve allows for a squatter top hamper which is less vulnerable to damage.